High-entropy Prussian blue analogue composite MXene electrode material and preparation method and application thereof

Abstract

The invention discloses a high-entropy Prussian blue analogue composite MXene electrode material and a preparation method and application thereof. The preparation method comprises the following steps: mixing LiF and concentrated hydrochloric acid, adding an MAX phase material, and reacting to obtain an MXene precursor; the preparation method comprises the following steps: dispersing a manganese salt, a ferrous salt, a cobalt salt, a nickel salt, a copper salt and an MXene precursor in deionized water to obtain a solution A, dispersing a hexacyanoferrate in deionized water to obtain a solution B, dropwise adding the solution A into the solution B to obtain a solution C, standing, aging, centrifuging, and freeze-drying to obtain the high-entropy Prussian blue analogue composite MXene electrode material. The high-entropy Prussian blue analogue composite MXene electrode material prepared by the invention is used as a cathode for capacitive deionization, shows the desalination capacity of 106.3 mg g <-1 > and the desalination rate of 36.2 mg g <-1 > min <-1 > under the voltage of 1.2 V, does not have performance degradation after 100 adsorption and desorption cycles, and has excellent desalination performance.

Description

Technical Field

[0001] The present invention relates to the technical fields of capacitive deionization technology and seawater desalination technology, and particularly relates to a high-entropy Prussian blue analogue composite MXene electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, capacitive deionization technology (CDI) has become a research hotspot in the field of seawater desalination due to its characteristics such as low energy consumption, simple operation, and environmental friendliness.

[0003] The core of achieving high performance in a CDI system lies in the structural design and optimization of electrode materials. Two-dimensional transition metal carbides / nitrides (MXene) materials exhibit excellent ion intercalation performance and high metallic conductivity (up to 6500 S cm -1 ), and their volumetric capacitance can reach 900 F cm -3 .

[0004] Chinese Patent with publication number CN114804110A discloses a grape-like MXene material with a three-dimensional interconnected hollow structure, its preparation, and application. Through the template method and microbial-assisted assembly method, a grape-like MXene with a three-dimensional hollow structure is constructed. This material has a large specific surface area, but the highest desalination rate is only 8 mg g -1 min -1 , and the desalination performance is limited.

[0005] CN113881040A discloses a preparation method of a two-dimensional MXene / polydopamine composite desalination electrode material, including the following steps: (1) Block copolymer self-assembly: First, the triblock copolymer poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) PEO20-b-PPO70-b-PEO20 is used to self-assemble in solution to form cylindrical micelles as mesoporous soft templates; (2) Preparation of mesoporous MXene / polydopamine two-dimensional composite nanosheets mPDA / MXene. Using P123 as a soft template, mesoporous channels are introduced on both sides of MXene, making the material have a larger internal active specific surface area and ion transport channels, which is expected to improve the electrochemical performance and has the application prospect of capacitive deionization. However, its desalination capacity and desalination speed only reach 48 mg g -1 and 1.33 mg g -1 min -1 , and still need to be further improved.

[0006] In the application of seawater desalination based on capacitive deionization technology, the existing MXene-based composite electrode materials have problems of few ion adsorption sites and poor stability of electrode materials, resulting in limited desalination performance at the current stage. Therefore, for the MXene-based composite electrode materials for seawater desalination based on capacitive deionization technology, material optimization still needs to be continuously carried out. Summary of the Invention

[0007] Aiming at the problems of low desalination capacity and slow desalination rate of existing electrode materials in capacitive deionization technology, the present invention provides a preparation method of a high-entropy Prussian blue analogue composite MXene electrode material with ultra-high desalination capacity and ultra-fast desalination rate. Using this composite material as the cathode of hybrid capacitive deionization can effectively solve the problems of unstable structure and low capacitance of MXene-based electrode materials during application, and exhibit excellent desalination performance.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A preparation method of a high-entropy Prussian blue analogue composite MXene electrode material, comprising the steps of:

[0010] Step 1, mix LiF and concentrated hydrochloric acid under ice bath, add MAX phase material to the mixed solution for reaction, centrifuge and wash the product, disperse it in water, and then obtain a MXene nanosheet dispersion after ultrasonic treatment and centrifugation, and freeze-dry to obtain a MXene precursor;

[0011] Step 2, disperse manganese salt, ferrous salt, cobalt salt, nickel salt, copper salt and MXene precursor in deionized water to obtain solution A, disperse ferrocyanide salt in deionized water to obtain solution B, drop solution A into solution B to obtain solution C, and after static aging, carry out centrifugation and freeze-drying treatment to prepare the high-entropy Prussian blue analogue composite MXene electrode material.

[0012] With the help of the layered structure and conductive framework of MXene nanosheets, this invention provides structural support for high-entropy Prussian blue analogues (HEPBAs) nanoparticles. Under the synergistic effect of the pseudocapacitance characteristics of multiple active centers of high-entropy Prussian blue analogues and the conductive network of MXene nanosheets, the high-entropy Prussian blue analogue composite MXene electrode material achieves faster electron transport and ion diffusion during the CDI desalination process, significantly improves the structural stability of the composite material, and prolongs the lifespan of the electrode material. The preparation principle of the high-entropy Prussian blue analogue composite MXene electrode material provided by this invention is as follows: The Al layer in MXene is selectively etched away by strong acid. Subsequently, the closely stacked MXene sheets are separated through ultrasonic treatment, and the interlayer water molecules are removed through freeze-drying treatment, finally obtaining a two-dimensional nanosheet layered MAX precursor with an increased specific surface area and a good pore structure. Subsequently, under the action of a complexing agent, in a high-entropy system with coexisting multiple metal ions, through precise optimization of the electronic structure of the high-entropy alloy material by the Mn content, multiple redox electron pairs are formed by different metal ions during electrochemical applications. The layered structure of the MXene sheets provides nucleation sites for the high-entropy Prussian blue material, promoting the uniform deposition of metal ions, thereby enhancing the interfacial stability of the composite material as well as the performance of fast electron transport and ion diffusion, and obtaining excellent desalination performance.

[0013] The mass ratio of the total mass of the manganese salt, ferrous salt, cobalt salt, nickel salt, and copper salt to the mass of the MXene precursor is 1 - 5:1. Preferably, the mass ratio is 2 - 4:1. When the proportion of HEPBAs is too high, it may lead to the aggregation and accumulation of HEPBAs particles. An appropriate proportion can provide more surface areas through the MXene nanosheets, which is beneficial to the uniform distribution of HEPBAs, thereby improving the structural stability of the composite material and contributing to the improvement of desalination performance.

[0014] The molar amount of the manganese salt accounts for 20 - 80% in the total molar amount of the manganese salt, ferrous salt, cobalt salt, nickel salt, and copper salt. To obtain high desalination performance, this invention regulates the electronic structure of high-entropy Prussian blue analogues by adjusting the Mn content, and conducts structural regulation on the obtained high-entropy Prussian blue analogue composite MXene electrode material. By precisely adjusting the feeding amount of the MXene precursor, the specific surface area of the high-entropy Prussian blue analogue composite MXene electrode material is improved, and the electron transport during the desalination process is optimized through the adjustment of interfacial interactions to enhance the desalination performance. Preferably, the molar proportion of the manganese salt is 40 - 80%, and more preferably 50 - 70%.

[0015] The molar ratio of the ferrous salt, cobalt salt, nickel salt, and copper salt is 0.5 - 2:0.5 - 2:0.5 - 2:0.5 - 2.

[0016] In Step 2, the molar ratio of the ferricyanide salt to the total molar amount of the manganese salt, ferrous salt, cobalt salt, nickel salt, and copper salt is 2 - 8:10.

[0017] The MAX phase material includes one of Ti3AlC2, Ti2AlC, and Mo2AlC.

[0018] In Step 1, the mass ratio of MAX to LiF is (0.3 - 1.5) g:(0.5 - 2) g, and the mass - volume ratio of LiF to concentrated hydrochloric acid is (0.5 - 2) g:(3 - 20) mL; when the content of LiF is too low, the concentration of F - ions is insufficient, the etching reaction slows down, the metal layer in MAX is not completely peeled off, the etching effect is not significant, resulting in unclear delamination of MXene and insufficient exposure of the active sites of the composite material. When the content of LiF is too high, it will cause over - etching, resulting in too many structural defects on the surface of MXene nanosheets, hindering the ion transport in the desalination process, and ultimately reducing the desalination performance of the material.

[0019] In Step 1, the mixing time is 10 - 60 min, the reaction time is 15 - 30 h, and the reaction temperature is 20 - 50 °C;

[0020] After the reaction in Step 1, the centrifugation speed is 3000 - 12000 rpm, the time is 5 - 20 min, the volume of deionized water required to disperse the precipitate is 20 - 60 mL, the ultrasonic time is 2 - 4 h, and the power is 100 - 300 w; then the centrifugation speed is 2000 - 5000 rpm, and the re - centrifugation time is 1 - 3 h.

[0021] In Step 2, a complexing agent is also included. The complexing agent includes one of sodium citrate and potassium citrate, and the molar ratio of the complexing agent to the manganese salt is 1 - 10:1.

[0022] The manganese salt includes one or more of manganese chloride, manganese acetate, or manganese nitrate and their hydrates;

[0023] The ferrous salt includes one or more of ferrous chloride, ferrous sulfate and their hydrates;

[0024] The cobalt salt includes one or more of cobalt chloride, cobalt acetate, or cobalt nitrate and their hydrates;

[0025] The nickel salt includes one or more of nickel chloride, nickel acetate, or nickel nitrate and their hydrates;

[0026] The copper salt includes one or more of copper chloride, copper acetate, or copper nitrate and their hydrates;

[0027] The ferricyanide salt includes one or more of potassium ferricyanide, sodium ferricyanide and their hydrates.

[0028] In step 2, the static aging is performed at room temperature for 1-5 hours.

[0029] The present invention also provides a high-entropy Prussian blue analogue composite MXene electrode material obtained according to the preparation method of the high-entropy Prussian blue analogue composite MXene electrode material.

[0030] The present invention also provides the application of the high-entropy Prussian blue analogue composite MXene electrode material in capacitive deionization of seawater.

[0031] The high entropy Prussian blue analogue composite MXene electrode material provided by the present invention is used as a CDI cathode and exhibits a high conductivity of 106.3 mg g at a voltage of 1.2 V. -1 The desalination capacity and 36.2 mg g -1 min -1 The desalination rate was high, and there was no desalination performance degradation after 100 adsorption and desorption cycles, showing excellent desalination performance.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The present invention utilizes the layered structure of MXene nanosheets to provide nucleation sites and structural support for high-entropy Prussian blue materials, promotes uniform deposition of metal ions, enhances the interfacial stability of the composite material, significantly improves the structural stability of the composite material, and prolongs the life of the electrode material.

[0034] (2) The present invention precisely optimizes the electronic structure of high-entropy metal alloys through the Mn content. Different metal ions form multiple redox electron pairs in electrochemical applications, and the composite material obtains more active sites and faster electron transport and ion diffusion.

[0035] (3) Under the synergistic effect of the pseudocapacitive properties of the high-entropy Prussian blue analogue multimetallic active center and the conductive network of MXene nanosheets, the high-entropy Prussian blue analogue composite MXene electrode material obtains excellent desalination performance in the CDI desalination process. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 HEPBAs / Ti3C2T prepared in Example 1 x Scanning electron micrograph of the electrode material.

[0037] Figure 2 This is a Lagung diagram of the desalination performance of the materials prepared in Example 1 and Comparative Examples 1-2 in Application Example 1.

[0038] Figure 3 This is a cyclic stability diagram of the materials prepared in Example 1 and Comparative Examples 1-2 in Application Example 1.

[0039] Figure 4 Desalination performance diagrams of the HEPBAs / Ti3C2T electrode materials prepared with different dosages of manganese salts in Application Example 2 x

[0040] Figure 5 Desalination performance diagrams of the HEPBAs / Ti3C2T electrode materials prepared with different dosages of Ti3C2T precursors in Application Example 3 x x Detailed implementation manners

[0041] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Those skilled in the art who make modifications or equivalent replacements on the basis of understanding the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall all be covered within the protection scope of the present invention.

[0042] The raw materials used in the following detailed implementation manners are all purchased from the market.

[0043] Example 1

[0044] Step 1: Take 15 mL of 12 M concentrated hydrochloric acid in a reaction kettle, and slowly add 1 g of LiF under stirring conditions. Weigh 0.5 g of Ti3AlC2 and slowly add it to the above solution, stir well for 15 min, and react at 35 °C for 20 h. After the reaction, the solution is centrifuged at 9000 rpm for 5 min, and the centrifugal washing with deionized water is repeated until the pH of the supernatant is approximately 6, and the precipitate is retained. The above precipitate is dispersed in 50 mL of deionized water, ultrasonically treated at room temperature for 3 h, and the obtained suspension is centrifuged at 3500 rpm for 1 h, and the supernatant is retained and freeze-dried to obtain an MXene precursor, denoted as Ti_{3}C_{2}T x .

[0045] ​​​Step 2: Weigh 3 mmol of MnCl₂·4H₂O, 0.5 mmol of FeCl₂·4H₂O, 0.5 mmol of CuCl₂·2H₂O, 0.5 mmol of NiCl₂·6H₂O, 0.5 mmol of CoCl₂·6H₂O and 330 mg of MXene precursor into a beaker, add 200 mL of deionized water, and disperse evenly by ultrasonic to obtain Solution A; weigh 25 mmol of sodium citrate and 10 mmol of Na₄[Fe(CN)₆] into a beaker, add 200 mL of deionized water, and disperse evenly by ultrasonic to obtain Solution B. Under stirring conditions, slowly drip Solution B into Solution A, let it stand and age for 3 h, wash with deionized water, centrifuge to collect the precipitate, and freeze-dry to obtain the high-entropy Prussian blue analogue composite MXene electrode material, denoted as HEPBAs / Ti₃C₂T x .

[0046] The scanning electron microscopy analysis was performed on the high-entropy Prussian blue analogue composite MXene electrode material prepared in this example, and the results are as Figure 1 shown. It can be seen from Figure 1 that the high-entropy Prussian blue analogue grows uniformly in the form of nanoparticles on the surface of MXene nanosheets. The particle size of the high-entropy Prussian blue analogue is about 300 nm, and the size of Ti₃C₂T x nanosheets is about 5 μm.

[0047] Comparative Example 1[[ID=1*]]

[0048] According to the process of Example 1, without performing Step (2), the MXene precursor obtained in Step (1) is denoted as Ti₃C₂T x .

[0049] Comparative Example 2

[0050] According to the process of Example 1, without performing Step (1), and without adding the Ti₃C₂T x precursor in Step (2), the high-entropy Prussian blue analogue is obtained, denoted as HEPBAs.

[0051] Example 2

[0052] According to the process of Example 1, the difference is that in Step (2), the total molar amount of metal salts in Solution A is kept at 5 mmol, the molar amounts of FeCl₂, CuCl₂, NiCl₂ and CoCl₂ are the same, and the molar amount of MnCl₂ is changed to 0.5 mmol, 1 mmol, 2 mmol, 4 mmol, corresponding to HEPBAs / Ti₃C₂T x -10%, HEPBAs / Ti₃C₂T x -20%, HEPBAs / Ti₃C₂T x-40%, HEPBAs / Ti3C2T x -80%. The high-entropy Prussian blue analogue composite MXene electrode material prepared in Example 1 is denoted as HEPBAs / Ti3C2T x -60%.

[0053] Example 3

[0054] According to the process of Example 1, the difference is that in step (2), the dosages of MXene precursors are 250 mg and 500 mg, corresponding to HEPBAs / Ti3C2T x -4:1, HEPBAs / Ti3C2T x -2:1. The high-entropy Prussian blue analogue composite MXene electrode material prepared in Example 1 is denoted as HEPBAs / Ti3C2T x -3:1%.

[0055] Application Example 1

[0056] Hybrid capacitive deionization was adopted in the experiment. The electrolyte was 500 ppm NaCl solution, and the negative electrode materials were the high-entropy Prussian blue analogue composite MXene electrode materials prepared in Example 1 and Comparative Examples 1-2. The active material, carbon black, and polyvinylidene fluoride were mixed and ground evenly according to the mass ratio of 8:1:1, and then dispersed in N-methylpyrrolidone to prepare the catalyst ink, which was coated on the carbon paper at a loading of 2 mg cm -2 and then dried at 40 °C for 24 h to prepare the cathode of the hybrid capacitive deionization device. Similarly, the above-mentioned active material was replaced with commercial activated carbon to prepare the anode. A constant voltage of 1.2 V was applied at both ends of the hybrid capacitive deionization device, and a conductivity meter was used to monitor the change in the conductivity of the electrolyte, and the desalination performance of the electrode material was calculated.

[0057] After the adsorption experiment, the short circuit was used to start the desorption experiment. When the conductivity reading of the electrolyte returned to the initial value and stabilized, the desorption process was completed, and at this time, an adsorption / desorption cycle was completed. At a constant voltage of 1.2 V, the salt solution continuously flowed into the hybrid capacitive deionization device at a fixed flow rate through a peristaltic pump, and multiple adsorption / desorption cycle experiments were carried out to monitor the change in conductivity in each cycle to evaluate the desalination stability of the electrode material.

[0058] As Figure 2 shown, the HEPBAs / Ti3C2T x electrode material has a desalination rate of 36.2 mg g -1 min -1 at a voltage of 1.2 V, which is significantly better than that of Ti3C2T x (5.5 mg g -1 min -1) and HEPBAs (24.1 mg g -1 min -1 )。As Figure 3 shown, compared with HEPBAs and Ti3C2T x , the desalination capacity of the HEPBAs / Ti3C2T x electrode material still remained at 106.3 mg g -1 after 100 adsorption / desorption cycles, significantly superior to the HEPBAs and Ti3C2T x electrode materials used alone. It shows that the HEPBAs / Ti3C2T x electrode material has broad application prospects in the application of hybrid capacitive deionization desalination.

[0059] Application Example 2

[0060] According to the process of Application Example 1, the materials prepared in Example 1 and Example 2 were tested in the application example, and the results are as Figure 4 shown. The molar amount of MnCl2 was changed to 0.5 mmol, 1 mmol, 2 mmol, 3 mmol, 4 mmol, corresponding to HEPBAs / Ti3C2T x -10%, HEPBAs / Ti3C2T x -20%, HEPBAs / Ti3C2T x -40%, HEPBAs / Ti3C2T x -60%, HEPBAs / Ti3C2T x -80%. It can be seen from Figure 4 that when a constant voltage of 1.2 V was applied, the HEPBAs / Ti3C2T x -60% prepared in Example 1 showed the highest desalination capacity, which was 106.3 mg g -1 . The desalination capacities of HEPBAs / Ti3C2T x [[ID=4x2]] -10%, HEPBAs / Ti3C2T x -20%, HEPBAs / Ti3C2T x -40%, HEPBAs / Ti3C2T x -80% were 36.1, 52.7, 69.1, 43.8 mg / g respectively.

[0061] Application Example x3

[0062] According to the process of Application Example 1, the electrode materials prepared in Example 1 and Example 3 were tested in the application example, and the results are as Figure 5 shown. Ti3C2T xThe dosages of the precursor are 250 mg, 330 mg, and 500 mg, corresponding to HEPBAs / Ti3C2T x -4:1, HEPBAs / Ti3C2T x -3:1, HEPBAs / Ti3C2T x -2:1. As Figure 5 shown, in a 500 ppm NaCl solution at a voltage of 1.2 V, the composite electrode material HEPBAs / Ti3C2T prepared with a precursor dosage of 330 mg in Example 1 x -3:1 exhibited the highest desalination capacity of 106.3 mg g x . The capacities corresponding to HEPBAs / Ti3C2T -1 -4:1 and HEPBAs / Ti3C2T x -2:1 were 75.3 and 100.0 mg g, respectively x . -1 ​

Claims

1. A method for preparing a high-entropy Prussian blue analogue composite MXene electrode material, characterized in that: Including steps: Step 1: LiF and concentrated hydrochloric acid are mixed in an ice bath, and MAX phase material is added to the mixture for reaction. The product is centrifuged, washed, and dispersed in water. After sonication and centrifugation, a MXene nanosheet dispersion is obtained, which is freeze-dried to obtain a MXene precursor. Step 2: Disperse manganese salt, ferrous salt, cobalt salt, nickel salt, copper salt and MXene precursor in deionized water to obtain solution A, disperse ferrocyanide salt in deionized water to obtain solution B, add solution A dropwise to solution B to obtain solution C, and after static aging, centrifuge and freeze-dry to obtain the high-entropy Prussian blue analogue composite MXene electrode material.

2. The method for preparing a high-entropy Prussian blue analogue composite MXene electrode material according to claim 1, characterized in that: The mass ratio of the total mass of the manganese salt, ferrous salt, cobalt salt, nickel salt, and copper salt to the MXene precursor is 1-5:

1.

3. The method for preparing a high-entropy Prussian blue analogue composite MXene electrode material according to claim 1, characterized in that: The molar amount of the manganese salt accounts for 20-80% of the total molar amount of the manganese salt, the ferrous salt, the cobalt salt, the nickel salt and the copper salt.

4. The method for preparing a high-entropy Prussian blue analogue composite MXene electrode material according to claim 1, characterized in that: The molar ratio of the ferrous salt, cobalt salt, nickel salt and copper salt is 0.5-2:0.5-2:0.5-2:0.5-2; And / or, in step 2, the molar ratio of the ferricyanide salt to the total molar ratio of the manganese salt, the ferrous salt, the cobalt salt, the nickel salt, and the copper salt is 2-8:

10.

5. The method for preparing a high-entropy Prussian blue analogue composite MXene electrode material according to claim 1, characterized in that: The MAX phase material includes one of Ti3AlC2, Ti2AlC, and Mo2AlC.

6. The method for preparing a high-entropy Prussian blue analogue composite MXene electrode material according to claim 1, characterized in that: In step 1, the mass ratio of MAX to LiF is (0.3-1.5) g:(0.5-2) g, and the mass volume ratio of LiF to concentrated hydrochloric acid is (0.5-2) g:(3-20) mL; And / or, in step 1, the mixing time is 10-60 min, the reaction time is 15-30 h, and the reaction temperature is 20-50° C.; And / or, after the reaction in step 1 is completed, the centrifugal speed is 3000-12000 rpm, the time is 5-20 min, the volume of deionized water required for dispersion and precipitation is 20-60 mL, the ultrasonic time is 2-4 h, the power is 100-300 W; the centrifugal speed is then 2000-5000 rpm, and the centrifugal time is then 1-3 h; And / or, step 2 further includes a complexing agent, the complexing agent includes one of sodium citrate and potassium citrate, and the molar ratio of the complexing agent to the manganese salt is 1-10:

1.

7. The method for preparing a high-entropy Prussian blue analogue composite MXene electrode material according to claim 1, characterized in that: The manganese salt includes one or more of manganese chloride, manganese acetate or manganese nitrate and hydrates thereof; The ferrous salt includes one or more of ferrous chloride, ferrous sulfate and hydrates thereof; The cobalt salt includes one or more of cobalt chloride, cobalt acetate or cobalt nitrate and hydrates thereof; The nickel salt includes one or more of nickel chloride, nickel acetate or nickel nitrate and hydrates thereof; The copper salt includes one or more of copper chloride, copper acetate or copper nitrate and hydrates thereof; The ferrocyanide salt includes one or more of potassium ferrocyanide, sodium ferrocyanide and hydrates thereof.

8. The method for preparing a high-entropy Prussian blue analogue composite MXene electrode material according to claim 1, characterized in that: In step 2, the static aging is performed at room temperature for 1-5 hours.

9. A high-entropy Prussian blue analogue composite MXene electrode material obtained according to the preparation method of the high-entropy Prussian blue analogue composite MXene electrode material according to any one of claims 1 to 8.

10. Use of the high-entropy Prussian blue analogue composite MXene electrode material according to claim 9 in capacitive deionization of seawater.

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